Gripper for supporting substrate in a vertical orientation

ABSTRACT

A gripper assembly is provided which supports a substrate in a vertical orientation. The gripper assembly&#39;s end effectors contact only the edge of the substrate. In a first aspect the end effectors each comprise a first pair of opposed surfaces and an second pair of opposed surfaces, all of which simultaneously contact the substrate, holding the substrate in a clamp-type manner. In a second aspect the end effectors each comprise a lower pair of opposed surfaces which simultaneously contact the substrate, and an upper pair of opposed surfaces, larger than the thickness of the substrate, which limit the substrate from horizontal tilting. In the second aspect the end effectors can close at a first elevation where they do not contact the substrate, and can then elevate to gently contact and support the substrate in a pocket-like manner. In a third aspect one of the end effectors has two pairs of opposed surfaces which simultaneously contact the substrate, and the other end effector has two pairs of opposed surfaces which limit the substrate from horizontal tilting. In any aspect no moving parts are required to limit the substrate&#39;s vertical and horizontal movement. In a further aspect, fingers to which the end effectors are coupled, are bent so that the gripper is not positioned above the substrate.

[0001] This application is a continuation of U.S. patent applicationSer. No. 09/559,889, filed Apr. 26, 2000, which is hereby incorporatedby reference herein in its entirety.

BACKGROUND OF THE INVENTION

[0002] When designing an automated semiconductor substrate handler,three main concerns prevail; 1) substrate handler reliability; 2)substrate handler particle generation and potential for substratecontamination; and 3) substrate handler size. Each of these concerns isessentially aimed at reducing costs associated with damaged or defectivesubstrates. Increasing substrate handler reliability prevents substratedamage which can occur when a substrate is incorrectly grasped, etc.,and prevents downtime associated with repair and/or recalibration.Reducing particle generation helps reduce defects which result whenparticles contact substrate surfaces, and reducing substrate handlersize allows processing chamber openings to be smaller and to therebyreduce the possibility of particle entry to the chamber and thepossibility of substrate contamination thereby.

[0003] A major source of particles results when a substrate slides alongthe surface of the substrate handler's end effector. Accordingly, aftera wafer is placed/loaded onto an end effector, a pin or other holdingmechanism conventionally moves into place to secure the substrate andprevent the substrate from sliding against the end effector duringtransport. However sliding and the particles that result therefrom, mayoccur as part of the loading process. Further, the holding mechanisms,being moving parts themselves, can generate particles and can introducereliability issues, increasing substrate handler costs. Moreover, duringthe entire load and transfer process, particles and other contaminantsmay collect on the substrate or between the end effectors and thesubstrate.

[0004] Accordingly, a need exists for an improved substrate handler, andparticularly for a substrate handler having an improved end effectorwhich will reduce substrate sliding and the associated need for movingparts to control substrate sliding. Such a substrate handler and endeffector should be streamlined, and should reduce the probability ofcontaminant contact with substrate surfaces and/or the probability oftrapped contaminants between the end effector and the substrate.

SUMMARY OF THE INVENTION

[0005] The present invention provides an inventive gripper assemblyhaving a pair of fingers operatively coupled to the gripper so as tomove between an open and a closed position; each finger has an endeffector coupled thereto, and adapted to support a vertically orientedsubstrate therebetween. Each end effector has a first pair of opposedsurfaces and a second pair of opposed surfaces. Each pair of opposedsurfaces is adapted either to simultaneously contact the edge of avertically oriented substrate supported by the end effector, (clamp-typecontact) or to limit horizontal movement of a vertically orientedsubstrate supported by the end effectors (pockettype contact). Each ofthe opposed surfaces preferably does not move relative to the other. Apair of opposed surfaces that do not move relative to each other isreferred to herein as unitary, whether made of one or more pieces.Preferably, both the first and second opposed surfaces are radiused tomimic the circumference of the wafer so as to deter fluid andcontaminants from collecting between the substrate and the surfaces ofthe end effector.

[0006] In operation, the end effectors are positioned on opposite sidesof a vertically oriented substrate, and preferably pick up or grasp thesubstrate in either of the two manners described below. Specifically, inthe case of a gripper assembly configured for clamp-type contact, theend effectors are moved to a position at which the end effectors maystabily support the vertically oriented substrate. Thereafter, the endeffectors are closed such that the end effector's first and second pairsof opposed surfaces contact the substrate's edge and thereby support thesubstrate.

[0007] Similarly, in the case of a gripper assembly configured forpocket-type contact, the gripper assembly may simply close such that thetwo pairs of opposed surfaces positioned closest to the bottom edge ofthe substrate contact the substrate. Alternatively, the pocket-type endeffectors may move to a position in line with the substrate, yet at anelevation below which the pair of opposed surfaces would contact thesubstrate when the end effectors are in a closed position. Thiselevation may be entirely below the substrate or anywhere below thesubstrate's horizontal diameter. Thereafter the closed pair of endeffectors are elevated such that the end effectors' lower pairs ofopposed surfaces contact and support the substrate via the substrate'sedges. Note that a pocket type gripper need not have an open and closedposition, as the gripper may pick up and deposit a substrate by raisingand lowering around the substrate as will be apparent with reference tothe detailed description of the preferred embodiments.

[0008] The clamp-type gripper is advantageous because it is able tograsp wafers that are within a relatively wide tolerance of a desiredposition, and thus reduces the time required for initial robotcalibration and chamber alignment, as well as reducing the frequency andtime required for recalibration and alignment.

[0009] The pocket-type gripper is advantageous because it reduces therisk of substrate damage. The pocket-type grippers close below thesubstrate forming a pocket, and then elevate such that the substrategently contacts the bottom of the pocket (e.g., contacts the lower pairof opposed surfaces), and such that the upper pair of opposed surfacessurround the substrate and prevent the substrate from excessive tiltingin the horizontal direction. Accordingly, the only force applied to thesubstrate is a purely vertical lifting force, which tends to generatefewer particles than do multidirectional forces. Further, because thereis no external force opposing the vertical lifting force, the substrateis not acted on by external opposing forces, and is less likely to bedamaged.

[0010] When the gripper assembly is configured such that the gripper isat a higher elevation than the end effectors, the fingers are preferablybent such that the gripper is positioned to the front, back or mostpreferably the side of the substrate rather than directly above thesubstrate. Thus, particles from the gripper are less likely tocontaminate the substrate.

[0011] The end effectors of the inventive gripper assembly, whetherclamp-type or pocket-type, preferably have no moving parts, and aretherefore inexpensive and less likely to malfunction. Further, theabsence of moving parts enable a streamlined design, which in additionto the fact that the gripper assembly grasps a substrate by thesubstrate's edges, allows the inventive gripper assembly to movesubstrates through narrow openings such as those found in semiconductormanufacturing equipment.

[0012] Because the inventive gripper assembly is streamlined andinexpensive, and because the gripper assembly experiences reducedcalibration time, reduced particle generation, and reduced risk ofsubstrate damage, a substrate handler employing the inventive gripperassembly is ideally suited for semiconductor applications. Moreover,because the inventive gripper assembly supports a substrate in avertical orientation, contaminants are less likely to collect on thesubstrate's surfaces. Further contamination reduction may be achievedwith the use of radiused end effector surfaces which are radiused tomimic the circumference of the wafer, and thus may minimize or eliminatecontact with the front or back surface of the wafer and may contact onlythe beveled edge of the wafer.

[0013] Other objects, features and advantages of the present inventionwill become more fully apparent from the following detailed descriptionof the preferred embodiments, the appended claims and the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a side perspective view of a clamp-type end effector ofa first aspect of the inventive gripper assembly;

[0015]FIG. 1A is a cross-sectional view showing contact between asubstrate and opposed surfaces of the end effector of FIG. 1;

[0016]FIGS. 2A and 2B are front elevational views of a gripper assemblyemploying the clamp-type end effector of FIG. 1, showing the gripperassembly in an open and a closed position, respectively;

[0017]FIG. 3 is a side perspective view of a pocket-type end effector ofa second aspect of the inventive gripper assembly;

[0018] FIGS. 4A-B are front elevational views of a gripper assemblyemploying the pocket-type end effector of FIG. 3, showing the gripperassembly in a closed no-substrate-contact position and a closedsubstrate-contact position, respectively;

[0019]FIG. 5 is a front elevational view of an alternative pocket-typegripper assembly; and

[0020]FIG. 6 is a schematic side view of a substrate handler thatincludes the gripper assembly of FIGS. 4A-B.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021]FIG. 1 is a side perspective view of a clamp-type end effector 11of a first aspect of the inventive gripper assembly. The clamp-type endeffector 11 comprises a first pair of opposed surfaces 13 a-b, adaptedto simultaneously contact an edge of a vertically oriented substrate tobe supported thereby (FIGS. 2A-B), and a second pair of opposed surfaces15 a-b adapted to simultaneously contact a vertically oriented substrateto be supported thereby. The first pair of opposed surfaces 13 a-b andthe second pair of opposed surfaces 15 a-b preferably comprise a grooveadapted to support a substrate with minimum contact (e.g., via twoopposing points), such as a “v” shaped groove, as shown in FIG. 1A.Preferably, to deter particles and fluid contaminants from being trappedbetween the first pair of opposed surfaces 13 a-b and/or the second pairof opposed surfaces 15 a-b, and the substrate surface, the first pair ofopposed surfaces 13 a-b and the second pair of opposed surfaces 15 a-bare radiused to mimic the circumference of the wafer, and thus mayminimize or eliminate contact with the front or back surface of thewafer and may contact only the beveled edge of the wafer, as shown inFIG. 1. Further, the first pair of opposed surfaces 13 a-b and thesecond pair of opposed surfaces 15 a-b are preferably unitary, therebyminimizing moving parts.

[0022] The first pair of opposed surfaces 13 a-b and the second pair ofopposed surfaces 15 a-b preferably extend the same (with reference toFIG. 1 horizontal distance) distance x and the same (with reference toFIG. 1 vertical distance) distance y, from a point C which is to becentered on the substrate's diameter (e.g., in the configuration shownthe point C is to be centered on the substrate's horizontal diameter),such that when the point C is centered along the diameter of a substrate(where the clamp-type end effector 11 provides maximum stability) thefirst pair of opposed surfaces 13 a-b and the second pair of opposedsurfaces 15 a-b provide the only contact points with the substrate, andfor maximum stability, contact the substrate at equal distances from thesubstrate's diameter, as shown in FIGS. 2A-B.

[0023] FIGS. 2A-B are front elevational views of a gripper assembly 17which employs a pair of the end effector 11 of FIG. 1, and which showthe gripper assembly 17 in an open and a closed position, respectively.The gripper assembly 17 comprises a gripper 19, a pair of fingers 21 a-boperatively coupled to the gripper 19 so that the gripper 19 can movethe pair of fingers 2la-b between an open and a closed position. Coupledto the ends of the pair of fingers 21 a-b opposite the gripper 19, are apair of clamp-type end effectors 11 a-b, configured as described withreference to FIG. 1. The clamp-type end effectors 11 a-b are coupled tothe pair of fingers 21 a-b so that the first end effector 11 a's firstpair of opposed surfaces 13 a-b and second pair of opposed surfaces 15a-b are opposite the second end effector 11 b's first pair of opposedsurfaces 13 a-b and second pair of opposed surfaces 15 a-b,respectively.

[0024] Grippers for moving a pair of fingers between open and closedpositions are well known in the art, and are therefore not described indetail herein. Similarly, although shown in a scissors linkageconfiguration, the pair of fingers 21 a-b may be coupled in any mannerto achieve open and closed positions. However, in the scissors linkageconfiguration shown, the distance between the clamptype end effectors 11a-b in the open and closed position can be easily adjusted via a setscrew 23 which controls relative movement between the pair of fingers 21a-b by sliding back and forth within a slot 25, as is known in the art.

[0025] When the pair of fingers 21 a-b are configured in the scissorslinkage, the gripper 19 moves the base of the pair of fingers 21 a-bapart, causing the ends of the pair of fingers 2la-b to move apartthereby assuming an open position wherein the first pair of opposedsurfaces 13 a-b and the second pair of opposed surfaces are positionedfarther apart than the diameter of a substrate supported thereby (asshown in FIG. 2A). To assume the closed position, the gripper 19 movesthe base of the pair of fingers 21 a-b toward each other, causing theends of the pair of fingers 2la-b to move toward each other to aposition where the first pair of opposed surfaces 13 a-b and the secondpair of opposed surfaces 15-a-b are positioned such that each of thefirst pair of opposed surfaces 13 a-b and each of the second pair ofopposed surfaces 15 a-b contact the substrate S (as shown in FIG. 2B).Preferably, the lower of the two first pairs and the two second pairs ofopposed surfaces are positioned where the substrate S is narrower thanat its diameter (e.g., below the substrate's horizontal diameter oradjacent but off-set from the substrate's vertical diameter, etc.) Thus,due to the fact that the substrate's width increases as its diameter isapproached, the substrate S cannot slide downwardly through the lowerpair of opposed surfaces (e.g., with reference to FIG. 2 the first pairof opposed surfaces 13 a-b).

[0026] In operation a substrate handler (not shown) having the gripperassembly 17 coupled thereto, moves the gripper assembly 17 to a positionat which the clamp-type end effectors 11 a-b can stabily support thevertically oriented substrate S. The position at which the first pair ofopposed surfaces 13 a-b and the second pair of opposed surfaces 15 a-bcan stabily support the substrate S varies depending on the specificconfiguration of the first pair of opposed surfaces 13 a-b and thesecond pair of opposed surfaces 15 a-b (e.g., the distances x and y towhich the first pair of opposed surfaces 13 a-b and the second pair ofopposed surfaces 15 a-b extend, whether equal or differing distances,etc.). However, the position at which the clamptype end effectors 11 a-bcan stabily support the substrate S, preferably positions the center Cof the clamp-type end effector 11 a-b at the diameter of the substrate S(e.g., as shown in FIGS. 2A-B the horizontal diameter). Thereafter, thegripper assembly 17 assumes the closed position such that the first pairof opposed surfaces 13 a-b and the second pair of opposed surfaces 15a-b each contact the edge of the substrate S and the substrate S issupported thereby.

[0027] The clamp-type gripper assembly of FIGS. 2A-B can support asubstrate in a vertical orientation regardless of the position of thegripper relative to the substrate. Thus, by turning FIGS. 2A-B to viewthem from various orientations, one can view various orientations of thegripper assembly 17 which still support a vertically oriented substrateby its edges. The gripper assembly of FIGS. 2A-B are thus easilyadaptable to transfer substrates to and from variously configuredsubstrate supports. However, because most vertical substrate supportssupport a substrate along its lower hemisphere, the gripper assembly 17is preferably configured with the gripper 19 at a higher elevation thanthe end effectors 11 a-b. Accordingly, to reduce potential substratecontamination, the fingers 21 a-b are bent (e.g., as shown in FIGS.2A-B) to place the gripper 19 to the side of the substrate S (whereparticles are less likely to travel to the substrates front surface).Although less preferred, the fingers 21 a-b may be bent so as toposition the gripper 19 to the front, or preferably to the back of thesubstrate S.

[0028] The clamp type gripper assembly of FIGS. 2A-B may be able to pickup a flatted substrate regardless of its oreintation, because each ofthe end effectors 11 a-b may be sized so as to be longer than the lengthof a flat portion of a substrate to be gripped thereby. Accordingly atleast three of the pairs of opposed surfaces 13 a-b will contact aflatted substrate at any given time. Three points of contact aresufficient to securely grip a substrate.

[0029]FIG. 3 is a side perspective view of a pocket-type end effector 31of a pocket-type aspect of the inventive gripper assembly. Like theclamp-type end effector 11 of FIG. 1, the pocket-type end effector 31 ofFIG. 3 comprises a first and second pair of opposed surfaces, bestdescribed with reference to FIGS. 4A-B as a lower pair of opposedsurfaces 33 a-b adapted to simultaneously contact (e.g., via twoopposing points) an edge of a vertically oriented substrate S to besupported thereby. The pocket-type gripper assembly 31 also comprises anupper pair of opposed surfaces 35 a-b. However in the embodiment of FIG.3, the upper pair of opposed surfaces 35 a-b are adapted to limit thehorizontal movement of a vertically oriented substrate S supported bythe lower pair of opposed surfaces 33 a-b, rather than to clamp thesubstrate S. Thus the upper pair of opposed surfaces 35 a-b arepositioned far enough apart to allow some horizontal movement (both intoand out of the page).

[0030] Preferably both the lower pair of opposed surfaces 33 a-b and theupper pair of opposed surfaces 35 a-b comprise a groove adapted tominimize contact with the substrate S's front and back surfaces, such asa “v” shaped grove. Preferably, to deter particles and fluidcontaminants from being trapped between the lower pair of opposedsurfaces 33 a-b and/or the upper pair of opposed surfaces 35 a-b and thesubstrate S, the lower pair of opposed surfaces 33 a-b and/or the upperpair of opposed surfaces 35 a-b are radiused to mimic the circumferenceof the wafer, and thus may minimize or eliminate contact with the frontor back surface of the wafer and may contact only the beveled edge ofthe wafer, as shown in FIG. 3. Further, the lower pair of opposedsurfaces 33 a-b and the upper pair of opposed surfaces 35 a-b arepreferably unitary, thereby minimizing moving parts.

[0031] The lower pair of opposed surfaces 33 a-b preferably extend afurther horizontal distance (X₁), than do the upper pair of opposedsurfaces 35 a-b (X₂). Similarly, the lower pair of opposed surfaces 33a-b are located a greater vertical distance Y₁ from a point C which isto be centered on the substrate S's horizontal diameter, than are theupper pair of opposed surfaces 35 a-b (Y₂)

[0032] In this configuration a pair of pocket-type end effectors 31 a-bcan close when positioned along a narrower portion of the substrate S(e.g., below the elevation at which the lower pairs of opposed surfaces33 a-b contact the substrate S). Thus, when the end effectors 31 a-belevate, the upper pair of opposed surfaces 35 a-b (which do not extendinwardly as far as the lower pair of opposed surfaces 33 a-b) will notcontact the substrate S, as described further with reference to FIGS.4A-B. Alternatively, much like the clamp-type end effectors of FIGS.2A-B, the pockettype end effectors may open and close around thesubstrate S from an elevation at which the lower pair of opposedsurfaces will contact the substrate S when in the closed position.

[0033] FIGS. 4A-B are front elevational views of a gripper assembly 37employing a pair of the end effectors of FIG. 3 and showing the gripperassembly in a closed no-substrate-contact position and closedsubstrate-contact position, respectively. Aside from the pocket-type endeffectors 31 a-b, the gripper assembly 37 of FIGS. 4A-B is identical tothe gripper assembly 17 of FIGS. 2A-B. Accordingly, the descriptionthereof is not repeated with reference to FIGS. 4A-B.

[0034] In operation a substrate handler (not shown) having the gripperassembly 37 coupled thereto, lowers the gripper assembly 37 to anelevation below an elevation at which the lower pair of opposed surfaces33 a-b would intersect the substrate S when in the closed position.Thereafter, if the gripper assembly 37 is not already closed, thegripper assembly 37 assumes the closed position such that the upper pairof opposed surfaces 35 a-b close around the substrate S, but do notcontact the substrate S (FIG. 4A). The substrate handler (not shown)then elevates the gripper assembly 37 causing the lower pair of opposedsurfaces 33 a-b to gently contact and support the substrate S in apocket-like manner (FIG. 4B). The force exerted between the substrate Sand the lower pair of opposed surfaces 33 a-b preferably is purelyvertical and thus particle generation is minimized. During substratepick-up and transport, the upper pair of opposed surfaces 35 a-b (whichare further apart than the thickness of the substrate S's edge) do notcontact the substrate S unless the substrate S tilts horizontallyforward or backward.

[0035]FIG. 5 is a front elevational view of an alternative pocket-typegripper assembly 41. The pocket-type gripper assembly 41 is orientedsuch that the gripper 19 is positioned beside the substrate S. Asidefrom a bottom end effector 43 and a top end effector 45 the remainder ofthe gripper assembly 41 comprises components like those of FIGS. 1-4B.Accordingly, only those aspects of the gripper assembly 41 which differfrom the gripper assemblies 17 and 37 will be described with referenceto FIG. 5. Specifically, the bottom end effector 43 is positioned suchthat the first and second pair of opposed surfaces 33 a ₁-b ₁, 33 a ₂-b₂ are in a horizontal line. The first and second pair of opposedsurfaces 33 a ₁-b ₁, 33 a ₂-b ₂ are configured such that both opposingsurfaces simultaneously contact the substrate S to thereby support thesubstrate S. The top end effector 45 is also positioned such that thefirst and second pair of opposed surfaces 35 a ₁-b ₁, 35 a ₂-b ₂ are ina horizontal line. However, the first and second pair of opposedsurfaces 35 a ₁-b ₁, 35 a ₂-b ₂ of the top end effector 45 areconfigured like the upper pairs of opposed surfaces 35 a-b of FIGS.4A-B. Specifically, the first and second pair of opposed surfaces 35 a₁-b ₁, 35 a ₁-b ₁ of the top end effector 45 are adapted to limit thehorizontal movement of a vertically oriented substrate S supported bythe bottom end effector 43.

[0036] In operation the gripper assembly 41 assumes an open position andmoves to position the center points C of the top and bottom end effector43, 45 along the vertical diameter of the substrate S and then closes,as shown in FIG. 5. As the gripper assembly 41 closes, the bottom endeffector 43 gently contacts the substrate S and lifts it from thesubstrate support (not shown), and the top end effector 45 lowers to anelevation wherein the opposed surfaces thereof limit the horizontalmovement of the substrate S but do not clamp the substrate S (e.g., toan elevation wherein the substrate S is not inserted far enough withinthe groove formed by the opposed surfaces to contact the edges thereof,unless the substrate moves horizontally forward or backward).

[0037] The gripper of each of the gripper assemblies 17, 37 and 41,preferably are normally biased to a closed position (e.g., via a spring47 shown in FIG. 5). Thus, in the event a power failure occurs while thegripper assembly 17, 37, 41 supports a substrate S, the gripper assemblymaintains its closed position and does not drop the substrate S. Also,each of the gripper assemblies 17, 37 and 41, may be advantageouslycoupled to a substrate handler 51 having a moveable arm 53 for liftingand lowering the gripper assembly as shown in the schematic side view ofFIG. 6. Such a wafer handler may be advantageously used with the endeffectors described herein, and particularly with the pocket type endeffectors. Thus, as shown in FIG. 6, the gripper is at an elevationhigher than that of the end effectors, and at least one of the fingersis bent so that the gripper is not above the substrate supported by theend effectors.

[0038] The foregoing description discloses only the preferredembodiments of the invention, modifications of the above disclosedapparatus and method which fall within the scope of the invention willbe readily apparent to those of ordinary skill in the art. For instance,as previously mentioned, the end effectors 11 and/or 31, rather thanbeing unitary, may comprise moving parts which move the opposingsurfaces horizontally together and apart, so as to selectively contactthe substrate S. Further, although both the clamp-type and pocket-typeend effectors are preferably positioned along the diameter of thesubstrate S, other positions will also support the substrate. Of course,for both types of end effectors the lengths of the upper and lower pairsof opposed surfaces will vary according to the position at which theycontact the substrate. The opposed surfaces need not be v-shaped, anypair of surfaces which can support the substrate may be employed. Thus,the invention encompasses any gripper assembly which clamps or pockets avertically oriented substrate by contacting the substrate's edges.

[0039] Further, the clamp type end effectors may be advantageouslyemployed for gripping other, non-vertically oriented substrates (e.g.,horizontal, etc.). In such embodiments the substrate need not sliderelative to the end effectors (e.g., relative to a bottom plate of theend effector) as may occur in conventional horizontal end effectors.Specifically the inventive end effectors are each mounted to anindividual gripper finger which may move the respective end effector ina “tong” like motion rather than a pushing/sliding motion.

[0040] The gripper actuators and gripper finger configurations disclosedherein are merely exemplary. The gripper fingers need not cross, asshown herein, and the gripper actuators may comprise scissors typeactuators, sliding type actuators, etc.

[0041] Accordingly, while the present invention has been disclosed inconnection with the preferred embodiments thereof, it should beunderstood that other embodiments may fall within the spirit and scopeof the invention, as defined by the following claims.

The invention claimed is
 1. A method of handling a semiconductorsubstrate, comprising: positioning along opposite edges of asemiconductor substrate, a pair of end effectors adapted to support thesubstrate and coupled to ends of a pair of fingers that respectivelyextend along the opposite edges of the substrate; moving the endeffectors to a position at which the end effectors may stabily supportthe substrate; and closing the end effectors by moving the ends of thefingers toward each other such that the end effectors each contact anedge of the substrate.
 2. The method of claim 1 wherein closing the endeffectors such that the end effectors contact and support the substratecomprises contacting the substrate with a plurality of grooves, eachadapted to contact the substrate's edge at two opposing points.
 3. Themethod of claim 1 wherein closing the end effectors such that the endeffectors contact and support the substrate comprises contacting thesubstrate with four pairs of opposing surfaces.
 4. The method of claim 2wherein contacting the substrate with a plurality of grooves comprisescontacting the substrate with two supporting grooves, and wherein themethod further comprises preventing horizontal substrate tilting.
 5. Agripper assembly comprising: a gripper; a pair of fingers operativelycoupled to the gripper; and a pair of end effectors coupled to ends ofthe fingers and adapted to support a substrate therebetween, each endeffector comprising: a first pair of opposed surfaces adapted tosimultaneously contact an edge of a substrate to be supported by the endeffectors; and a second pair of opposed surfaces adapted tosimultaneously contact the edge of a substrate to be supported by theend effectors; wherein the fingers are adapted to respectively extendalong opposite edges of the substrate.
 6. A substrate handler,comprising: a mechanical arm capable of lifting and lowering; and thegripper assembly of claim 5 coupled to an end of the moveable arm. 7.The apparatus of claim 5 wherein the grippers are normally biasedclosed.
 8. The gripper assembly of claim 5 wherein the fingers aremovably linked to each other at a point between the gripper and the endsof the fingers.
 9. The gripper assembly of claim 5 wherein the first andsecond pair of opposed surfaces are radiused.
 10. A gripper assemblycomprising: a gripper; a pair of fingers operatively coupled to thegripper and adapted to extend along opposite edges of a substrate to besupported by the gripper assembly; and a pair of end effectors, onecoupled to an end of each of the fingers, adapted to support a substrateby its edges.
 11. The apparatus of claim 10 wherein the gripper is at anelevation higher than the end effectors, and at least one of the fingersis bent so that the gripper is horizontally displaced relative to asubstrate supported by the end effectors.
 12. The apparatus of claim 10wherein the grippers are normally biased closed.
 13. The gripperassembly of claim 10 wherein the fingers are movably linked to eachother at a point between the gripper and the ends of the fingers. 14.The gripper assembly of claim 10 wherein the first and second pair ofopposed surfaces are radiused.
 15. A gripper assembly comprising: agripper; a pair of fingers operatively coupled to the gripper; and apair of end effectors coupled to ends of the fingers and adapted tosupport a substrate therebetween, each end effector comprising: a firstpair of opposed surfaces and a second pair of opposed surfaces; whereinthe fingers are movably linked to each other at a point between thegripper and the ends of the fingers.
 16. The apparatus of claim 15wherein the first pair of opposed surfaces are radiused.
 17. Theapparatus of claim 15 wherein the second pair of opposed surfaces areradiused.
 18. The apparatus of claim 15 wherein the first and secondpairs of opposed surfaces of one of the end effectors are both adaptedto limit horizontal movement of a vertically oriented substratesupported by the first and second pairs of opposed surfaces of the otherof the end effectors.
 19. The apparatus of claim 15 wherein the secondpair of opposed surfaces of each of the end effectors are both adaptedto limit horizontal movement of a vertically oriented substratesupported by the first pair of opposed surfaces of each of the endeffectors.
 20. The apparatus of claim 15 wherein the first pair ofopposed surfaces of each of the end effectors and the second pair ofopposed surfaces of each of the end effectors are adapted tosimultaneously contact a substrate supported thereby.
 21. The apparatusof claim 15 wherein the grippers are normally biased closed.
 22. Thegripper assembly of claim 15 wherein the fingers are movably linked toeach other at a point between the gripper and the ends of the fingers.23. The gripper assembly of claim 15 wherein the first and second pairof opposed surfaces are radiused.
 24. The gripper assembly of claim 5wherein each of the pair of end effectors is sized so as to be longerthan the length of a flat portion of a substrate to be gripped thereby.25. The gripper assembly of claim 10 wherein each of the pair of endeffectors is sized so as to be longer than the length of a flat portionof a substrate to be gripped thereby.
 26. The gripper assembly of claim15 wherein each of the pair of end effectors is sized so as to be longerthan the length of a flat portion of a substrate to be gripped thereby.